Vaping may increase a person’s risk of suffering certain oral diseases, including oral cancer, according to the findings of a new study that examines the safety of electronic cigarettes.

In a study published in a recent issue of the medical journal PLOS One, researchers from the University of California, Los Angeles report that e-cigarette vapor caused approximately 85% of oral cells tested to die after exposure.

Researchers tested cultured cells from the outer most layer of the mouth. They exposed the cultured in vitro cells to two different brands of electronic cigarette vapor for 24 hours, using a machine built to use the popular devices like a human.

E-cigarette aerosols were found to significantly decrease intracellular levels of glutathione in a dose-dependent fashion. The e-cigarette vapor weakened the tissue’s natural defense mechanism and decreased the levels of glutathione antioxidants.

The toxic substances and reduced antioxidants caused roughly 85% of tested oral cells to die. Overall, researchers said the findings correlate to e-cigarette chemicals killing the top layer of skin cells in the oral cavity, the portion of the mouth behind the teeth and gums.

Researchers believe similar results would be found in tests on people and are planning to conduct a human study to confirm the study’s findings. They say the findings indicate e-cigarettes could increase a users risk of oral disease and oral cancer.

The findings come amid growing concerns over the unknown health impacts of vaping. E-cigarette use has exploded increased in recent years, especially among women and youth. More than 2.4 million middle and high school students in the U.S. use e-cigarettes in 2014, according to the U.S. Centers for Disease Control and Prevention (CDC).

The FDA’s Center for Tobacco Products released a report in March in the journal Tobacco Control that identified at least 92 reports of electronic cigarette explosions between 2009 and September 2015. However this report is considered to be outdated and severely unrealistic of the number of injuries caused by the devices.

More recent reports have shown 134 injuries caused by exploding electronic cigarettes from January 2016, according to FDA officials. Some of the most recent reports have come from younger children being injured by the devices.